{
语法百题 解题报告：
 http://git.oschina.net/et0662/sznoi-grammar/ 
}

function f(n:integer):longint;
begin
	if(n=0)then
		f:=1
	else
		f:=n*f(n-1);
end;

function c(n,m:integer):longint;
begin
	c:=f(n) div (f(m) * f(n-m));
end;

var
	i,j,n,m:integer;
begin
	readln(i,j,n,m);
	writeln(c(i,j)+c(n,m));
end.
